1. Field of the Invention
This invention relates to switching regulators and, more particularly, to reducing spectral noise due to ringing at the output of the switching regulators.
2. Description of the Related Art
Due to their efficiency and design flexibility, switching regulators are used to provide power in a variety of applications. One common type of switching regulator is a pulse width modulated (PWM) DC-to-DC regulator, in which switched current flows in an inductor and capacitor network. A control circuit may adjust the output voltage by adjusting switching times.
Generally, two modes may be used in PWM switching regulator circuits: continuous conduction mode and discontinuous conduction mode. In continuous conduction mode, the inductor current typically ramps up to a predetermined current and is then ramped down to another point, but the inductor current is typically not allowed to ramp down to zero. Conversely, when operating in discontinuous conduction mode (DCM), the inductor current may be allowed to ramp down to zero. However, depending on the switching configuration and parasitic circuit characteristics, when the inductor current ramps to zero, the switching action may cause undesirable frequency components (e.g., ringing) in the output waveform.
In many applications, the ringing may not be especially bothersome. However, when providing power in applications such as wireless communication or high-quality audio, for example, these undesirable frequency components may be unacceptable.